2006 F-150 5.4 L approx 40,000. I just did a coolant flush on my truck. Now, when I'm driving up normal hills, the coolant temperature goes up fast! Even when the air temp is around 50* the coolant temp got up to 198. Before the flush the engine coolant temp would run 188, and maybe 190. Then when I'm going down the hill the temperature drops drastically to about 176! Normal driving the temp sits at 190. I have had the new coolant in for about a week now, and I have been checking the level everyday. The first day I had to add a little, but since then the level has stayed the same.

I'm wondering could this be the thermostat? Or do you think air got into the system? Any help would be great. Thank you.

 

could be thermostat. air. something in front of radiator blocking only part of it. did they use 50/50 mix or pure antifreeze?

 

Sorry, did forget to mention. It was mixed 50/50. Used distilled water and coolant.

 

the only things i can think of is it being the thermostat, air, or something blocking the air from flowing through part of the radiator. if it was flushed with a machine i cant see it being air. i dont know about fords coolant but chevy dealers claim that if you flush out the dexcool an put in green then it'll run 10* hotter. which i cant see that with a good thermostat.

do you think that your just now noticing it? because i notice that once someone does work to a customers vehicle the customer looks for something that may be wrong. doesnt the 5.4 have like a 190* thermostat? if thats the case then it may just be the extra strain on the motor to get up the hill.

 

I did the flush my self, thats why I'm worried there might be air in it. Yes, the 5.4 has the 190* thermostat. I have the edge evo with the ECT displayed, and I watch the temps. Before It wouldn't raise as quick, and it defiantly did not get down to 176. I think I read that to make sure no air is in the system, remove the reservoir cap, and run the engine to normal opp temp. Is this correct? Thank you for your help tho.

 

But - there's no real direct sensor for coolant temperature is there? Doesn't the PCM "infer" the coolant temp from the CHT? (So air in the coolant circuit would not really be a factor, unless the coolant level was low).

The only thing I see odd is the big swings in temperature. The maximum you report is really about optimum. I monitor CHT on my Gryphon, and it's pretty steady in the neighborhood of 195-200. It will go up to 212-214 on steep mountain grades pulling in 2nd gear at 3-4000 rpm, but that's about it. The coolant gauge in the dash, never moves at all, once the engine is warmed up.

- Jack

 

burp the system.. . . Remove rad cap and give it a few good revs until all the air bubbles out of the system

 

Like Camaro said.. Run the engine to full op temp with the rad cap off... This should get out any air pockets, which is what it sounds like you have.

Mitch

 

slowly taking it up to high RPM and dropping it off quickly, then do a few quick rev-ups

 

Okay, I took the cap off at full temp and gave it a few revs. Didn't see any air bubbles come out, and didn't get to drive it after, so maybe tomorrow I'll be able to see if that worked. What are the signs and symptoms of a thermostat going bad?

 

I was of the understanding that these engines have a 195 thermostat. Mine runs from 194 to 198 all the time. They need that temp for efficiency. Troyer has stated before that these engines are most efficient, power wise, at around 210. I would just drive it.

 

I'm pretty sure if the thermostat's bad, it fails to the full open position (which makes sense - at least you can still drive your vehicle). This would give you a very slow warmup period and, if the outside temperature is cold, might make your truck stay at a colder than normal operating temperature.

- Jack

 

The 5.4 has a 195* thermo in it and as mentioned, these (and any other modern, new vehicle) runs optimally in the 200-215 range. I for one do not even see the beginnings of a problem with how your temps are running. I would bet dollars to donoughts that you're focusing on the temps more so that you ever did before simply because you changed something...I do it all the time, trust me! If you're correct in your temp comparisons, your truck is running better now than it was before you did this. I doubt I'd even try to burp it or any other suggestions that's been made...there's nothing wrong!!!

Keep in mind once again, a cooler engine is not a happy engine. Off subject (but an attempt to make you feel better) but I'd like to have a dollar every time I've seen a hotter thermostat fix an overheating problem. It's funny how many people truely do not understand the cooling system.

A thermostat can fail in any position...open or closed.

 

You're right, Galaxy! :o I guess I was remembering, once upon a time, when I replaced one with a new on that was designed to fail in the open position.

And, I agree with you that there's nothing wrong with his truck.

- Jack

 

MF- I don't know everything and I will freely admit that but I did run Dex-Cool in a '95 Taurus and a '95 F-150 when they were about 2 years old. I purchased both of them new and kept meticulous car of them and did not need to change the coolant but did so because I wanted long life in them. I won't go into the reason but I will never use Dex-Cool again. I did take the Dex-cool out of the Taurus but sold the F-150 with it still in. I can assure you there was not a trace of difference in the temp between Dex-Cool and the original Ford coolant. I think they (Chevy dealers) are full of prunes! My son also used it in a Dodge Caravan and Dodge pickup with NO change in temp. Maybe it only knows to change the temp if it being run in a Chevy. LOL By the way by the time I bought my '99 F-150, right in the manual it said in bold letters NOT to use the orange long life coolant in Fords. I think they knew more than Chevy.